Local oscillation device for a television receiver set

ABSTRACT

A harmonics generator for simultaneously producing a plurality of frequency spectra with the frequency separation equal to that of a plurality of channels, and a sweeping oscillator which initiates to sweep upon receipt of start-of-sweep signal to vary its oscillation frequency and which stops to sweep upon end-ofsweep signal to hold the frequency at the time the sweep was terminated are provided. A band pass filter is provided for deriving a beat signal when a predetermined frequency difference has appeared between the harmonics generator frequency and the sweeping oscillator frequency. Means are provided for deriving marker signals corresponding to respective channel positions from the output of the band pass filter. By counting the marker signals or by determining the coincidence of a marker signal with the tuning signal from a TV receiver set, a desired channel or channel through which electric wave is being transmitted may be selected and at the same time the frequency of the sweeping oscillator may be held constant by means of an automatic frequency control (AFC) circuit.

United States Patent 1 91 Fukuda et a1.

1451 Feb. 4, 1975 1 LOCAL OSCILLATION DEVICE FOR A TELEVISION RECEIVERSET [75] Inventors: Takeo Fukuda, Yokohama; Kenichi Torii, Tokyo; KazuoNishibayashi, Yokohama, all of Japan [731] Assignees Tokyo ShibauraElectric C0., Ltd.,

Kawasaki-shi, Japan [22] Filed: Mar. 20, 1973 [21] Appl. No.: 343,100

[30] Foreign Application Priority Data Nov. 9, 1972 Japan 47-112419 Nov.9, 1972 Japan 47-112420 [52] US. Cl 325/421, 325/470, 331/19 [51] Int.Cl. H03b 3/08 [58] Field Of Search 325/470, 469, 455, 418,

325/419, 420, 421, 422, 423, 464, 465, 468, 184; 331/4, 18, 19, 25, 34,178; 334/15, 29; 324/77 R, 77 CS Primary Examiner-Benedict V. SafourekAttorney, Agent, or Firm-Oblon, Fisher, Spivak, McC'lelland & Maier I57, ABSTRACT A harmonics generator for simultaneously producing aplurality of frequency spectra with the frequency separation equal tothat of a plurality of channels, and a sweeping oscillator whichinitiates to sweep upon receipt of start-of-sweep signal to vary itsoscillation frequency and which stops to sweep upon end-of-sweep signalto hold the frequency at the time the sweep was terminated are provided.A band pass filter is provided for deriving a beat signal when apredetermined frequency difference has appeared between the harmonicsgenerator frequency and the sweeping oscillator frequency. Means areprovided for deriving marker signals corresponding to respective channelpositions from the output of the band pass filter. By counting themarker signals or by determining the coincidence of a marker signal withthe tuning signal from a TV receiver set, a desired channel or channelthrough [56] References Cited which electric wave is being transmittedmay be se- UNITED STATES PATENTS lected and at the same time thefrequency of the 3,496,473 2/1970 Seppeler et al. 325/421 SweepingOscillator y be held Constant y means of 3,641,434 2/1972 Yates et al325/421 x an automatic frequency control (AFC) circui 3,654,557 4/1972Sakamoto et al. 325/463 X 3,736,513 5/1973 Wilson 325/421 13 Claims, 8Drawing Flg'lres .'Y FN N. FREQUENCY 72. INTERMEDIATE fvlDEo [ZCONVERTER FREQUENCY AMP I :T.2 L 1:ZJ f.i .'l,' l. HARMONICS E BAND M 1l GE} MIXER\ P AMP AFC X l e 5 7 e SWEEP l i -q I I 4 PULSE GE. 1

1... CONTROL i I 8 GE. I I Q TUNING I g F s R AND DETECTOR IPATENTEDFEB' 4IIII5 I SHEET 10F 5 QANTENNA FREQUENCY 72 INTERMEDIATEfvmEo K1 CONVERTER f FREQUENCY AMR 1 HARMONICS BAND XI I GE MIXER P AMPI 9 AFC\ I I e- 5 I a I DETECTOR A I SWEEP I0 I SC. CI I I I 4 PULSE GE.

CONTRO I I 5. GE. I I Q c TUNING l I s R DETECT R I I I II I2 I IFUNCTION I L KEY 1 2 I s 5 7 a s I BAND I-IARMONIC GE MIXER RAMP AFC NERT R 9 CO v E SWEEP DETECTOR PULSE; F I G. 2 I 3 GE.

. CONTROL 5. GE. I

I2 I I I o 0 I9 TUNING I 3- s R AND DETECTOR I6 I In CHANNEL 13 COUNTERDISPLAY I (I8 QgQI COMPARATOR MEMORY EI I I SHEET 2 [IF 5 PAIENIEI] FEB41975 FIG. 3

TO DETECTION CIRCUIT BAND IF. AMP.

RECTIFIER DIGIT KEY 1 I I I I I I I I |.L I

FIG. 4

LOCAL OSCILLATION DEVICE FOR A TELEVISION RECEIVER SET BACKGROUND OF THEINVENTION The present invention relates to a channel selection systemfor a TV receiver set, and particularly to such a channel selectionsystem which can reliably and rapidly select a desired channel or anon-the-air" channel where there exist a number of channels.

Where a huge number of broadcasting channels exist like in UHFbroadcasting system, it is necessary for a UHF receiver for receivingsuch broadcast to reliably and rapidly select a desired channel oron-the-air channel.

To achieve this, the following prior art has been known; a harmonicsgenerator for generating simultaneously a plurality of frequency spectrahaving frequency separation equal to that-of a number of chan'-- nels, asweeping oscillator whose oscillatingfrequency varies with thestart-of-sweep, and a phase comparator are provided. As the outputfrequency of the sweeping oscillator is varied, the phase relationshipbetween the frequency of the sweeping oscillator and the frequency ofthe harmonics generator is compared and a marker signal is derived eachtime the phases coincide. Since these marker signals occur incorrespondence with respective channel numbers, a desired channel numbermay be selected by counting those marker signals and immediatelystopping the sweep of the sweeping generator. Since the above operationis performed with a phase locking loop being established, the outputfrequency of the sweep generator afterth'e stop-of-sweep is maintainedconstant by means of the phase locking loop. r

With the above arrangement, however, in order to maintain theestablishment of the phase locking loop, the differential frequencybetween the signals supplied to the phase comparator from the harmonicsgenerator and the sweeping oscillator should be maintained within i100KHz. Since the sweeping oscillator oscillates in a broad band such as300 MHz, it is difficult, when taking the affects by the circuit timeconstants and various noises into consideratiom'to establish thevariation of the oscillating frequency in a narrow range such as in:tlOO KHz. As a result, the sweeping rate of the sweeping oscillatormust be set below a predetermined value. This means that longer time isrequired in channel selection operation before a normal receivingcondition is reached which of course is significant demerit in selectinga number of channels.

Furthermore, the phase locking loop of the type mentioned above is aptto be subjected to the affect of pulsing noise and is likely to becomeout-of-phase condition of the phase locking, in which case theoscillating frequency of the sweeping generator considerably deviatesfrom the predetermined frequency resulting in loss of receptioncondition. This trend is remarkable particularly in a broad bandoscillator, which is another serious demerit. 7

It is, therefore, an object of the present invention'to provide achannel selection'system for a TV receiver set which can select adesired channel reliably and rapidly without being affected by noiseseven when the sweeping rate of the sweeping oscillator is high and whichcan maintain the oscillating frequency of the sweeping oscillatorconstant after selecting the channel without being affected by noises.

SUMMARY OF THE INVENTION The present invention comprises a harmonicsgenerator for generating simultaneously a' plurality of frequencyspectra having frequency separation equal to that of a plurality ofchannels, a sweeping oscillator which initiates its sweep upon receiptof start-of-sweep signal and which varies its oscillating frequency, amixer for mixing the output of the harmonics generator with the outputof the sweeping oscillator, a band pass filter for deriving a beatsignal from the mixer when there exists a predetermined frequencydifference between the output frequency of the harmonics generator andthe output frequency of the sweeping oscillator, means for derivingmarker signals corresponding to respective channel positions from theoutput of the band pass filter, a channel selection switch for producingthe start-of-sweep signal, means in response to the marker signals afterthe start-of-sweep for selecting a desired channel and simultaneouslystopping the sweep, and an automatic frequency control (AFC) circuit formaintaining the output frequency of the sweeping oscillator after thesweep has been stopped.

Assuming that the frequency separation of the channel is 6 MHz, a localoscillation frequency (oscillating frequency of the sweeping oscillator)corresponding to, for example, the thirteenth channel is 530 MHz, andassuming that the corresponding frequency spectrum of the harmonicsgenerator is 528 MHz (this spectrum also having separation of 6 MHz),then the differential frequency therebetween is 2 MHz. It is easy to setthe frequency spectra of the harmonics generator at integral multiple of6 such as 528, 534, 822.

In order to derive a marker signal for each channel correspondingly,only odd numbered or even numbered ones of the beat signals are madeavailable.

In accordance with a feature of the present invention, means for settingthe number of desired channels such as memory means for storing numericvalue corresponding to that particular channel number is provided. Themarker signals are counted and when the count'reaches the numbercorresponding to the numeric value stored in the memory the sweepingoscillator is stopped to thereby select the desired channel. By the useof the AFC circuit, it is possible to stabilize the outputfrequency ofthe sweeping oscillator after the stop-of-sweep more rapidly and withless affect by the noises than will be the case where an automatic phasecontrol (APC) circuit is used.

In accordance with another feature of the present invention, it ispossible to automatically select the on-theair channel. This is achievedby stopping the sweep with a coincidence output of the marker signal anda tuning signal of the TV receiver set.

In accordance with further feature of the present invention,selectivesystem may be provided which selectively selects the desiredchannel and the on-the-air channel.

In accordance with further feature of the present invention, a digitalAFC circuit may be provided for maintaining the output frequency of thesweeping oscillator more stably after the end of channel selection.

In accordance with still further feature of the present invention, anantenna output and the harmonics generator output are sleectivelysupplied to the mixer by means of a switch, which is switched to theharmonics generator during selection of desired channel while it isswitched to the antenna circuit simultaneously with the channelselection whereby a portion of circuit arrangement may be used incommon.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing oneembodiment of the present invention in which an onthe-air channel isselected;

FIG. 2 is a block diagram showing another embodiment of the presentinvention in which a channel of desired number or an on-the-airchannelis selectively selected;

FIG. 3 is a block diagram showing further embodiment of the presentinvention in which an antenna output and an output of the harmonicsgenerator are switched by a switch to be supplied to a mixer;

FIG. 4 is a detailed illustration of the switch shown in FIG. 3;

FIG. 5 is a block diagram showing still another embodiment of thepresent invention which includes the switch shown in FIG. 3 and in whicha channel of desired number and an on-the-air channel are selectivelyselected;

FIG. 6 shows an arrangement ofa sweep voltage generator shown in FIG. 5;

FIG. 7 shows waveforms for illustrating the operation of the sweepvoltage generator shown in FIG. 6; and

FIG. 8 is a block diagram showing still further embodiment of thepresent invention in which a digital AFC circuit is provided forprecisely stabilizing the output frequency of the sweeping oscillatorafter selecting a desired channel.

DETAILED DESCRIPTION OF THE INVENTION For the clarification of thedescription, similar parts in the respective embodiments set forth belowhave the same reference numerals. In FIG. 1, a sweeping oscillator l iscontrolled by switch-in of a function key 2 via a control circuit 3(F.F. circuit) and a control signal generator 4 to increase theoscillating frequency continuously. The output of the sweepingoscillator is fed to (l) a frequency convertor circuit .71 of a TVreceiver set having an antenna 20 and an intermediate frequencyamplifier 72 which generates a video intermediate frequency signal 73and to (2) a mixer 5 with an output from a harmonics generator 6. Theharmonics generator 6 generates simultaneously a plurality of frequencyspectra having frequency separation equal to that between a plurality ofchannels. As an example, if the frequency separation of the channels is6 MHz, it generates simultaneously the frequency spectra of 528,534,540.. .(522 +6k) 822 MHz, where lt=l, 2, 3 50. When the function key2 is operated, the sweeping oscillator l commences its oscillationstarting from 528 MHz which is 2 MHz lower than the lowest channelfrequency and the oscillating frequency is continuously increased. Thusevery time the output frequency of the sweeping oscillator scans therespective frequency spectra of the harmonics generator 6, the mixer 5produces a beat signal. A band pass amplifier 7 amplifies only thosebeat signals which are near 2 MHz and feeds the amplified output to anAFC circuit 8 and a detector circuit 9. A pulse generator 10 shapes theoutput of the detector circuit 9 and supplies the (2n-l )th pulsesignals to one input terminal of an AND circuit 11, where n=l, 2, 3, 50.Thus, when the sweep is effected around a certain frequency spectrum ofthe harmonics generator with the output of the sweeping oscillator 1,since the beat signals appear at the positions 2 MHz above and belowthat frequency spectrum position, a pair of signals are derived from thedetector circuit 9-for the particular frequency spectrum. One of the twosignals, for example. the output signal at 2 MHz above the frequencyspectrum position is taken out of the detector circuit 9. The pulsesignal thus deliveredfrom the pulse generating circuit I0 represents thesignal indicating that of the plural frequency spectra of the harmonicsgenerator 6 which is being swept by the output frequency of the sweepingoscillator 1, namely, the position of said swept frequency spectrum.Accordingly, the above-mentioned pulse signal is hereinafter referred toas a marker signal.

As mentioned above, since each frequency spectrum of the harmonicsgenerator 6 corresponds to each channel frequency (each being separatedby 6 MHz), the marker signal will appear at a position 1.25 MHz apartfrom the lower extreme of the TV signal of, for example, 6 MHz bandwidth, that is at a position of the sweeping oscillation frequencyhigher than a carrier frequency of video signal by an intermediatefrequency (5875 MHz). As a result, themarker signals can indicaterespective channel positions.

A tuning signal from a tuning detector circuit 12 of the TV receiver setis applied to the other input of the AND circuit which produces astop-of-sweep signal when the marker signal from the pulsegeneratorcircuit II and the tuning signal from the tuning detectorcircuit concurrently occur. When the stop-of-sweep signal is applied tothe control circuit (F.F. circuit) 3, the AFC circuit 8 is actuated bythe signal from the control circuit 3, and the output of the AFC circuitis fed to the control signal generator circuit 4, the output of whichserves to maintain the output frequency of the sweeping oscillatorstably.

In the above arrangement, the function switch 2 is coupled to a setterminal S of the control circuit 3 such as F.F. circuit and the outputof the AND circuit 11 is coupled to reset terminal R of the controlcircuit 3. A signal from a set output terminal Q activates the con trolsignal generator circuit 4 which supplies a sweeping voltage to thesweeping oscillator I to start the sweep. During the increase of theoutput frequency of the sweeping oscillator l, the AND circuit producesno output until the receiver set tunes because no output is producedfrom the tuning detector circuit 12 even if the marker signal is appliedfrom the pulse generator circuit 10 to the AND circuit 11. Thus, theoutput of the F.F. circuit remains in the illustrated conditionpermitting the sweep to continue. If the difference between the outputfrequency of the sweeping oscillator l and the frequency of anon-the-air channel (i.e., intermediate frequency signal 73 which isconnected to tuning detector 12) reaches a predetermined relationship,the output signal of the tuning detector circuit 12 is applied to theAND circuit 11 and the marker signal corresponding to that channel isalso applied to the AND circuit 11. The output of the AND circuit 11 isapplied to the reset terminal R of the F.F. circuit 3 to reset the sameso that the sweep of the sweeping generator is stopped. Since the outputQ of the F.F. circuit reverses to Q at this time, the AFC circuit 8 isactivated to maintain the output frequency of the sweeping oscillator 1stably.

In accordance with the present invention, the sweep is stopped by merelydepressing the function key 2 and only when the marker signal and thetuning signal coincide so that the selection of on-the-air channel iseffected without erroneous operation and within an extremely short time.More particularly, the marker pulse always has a fixed level and appearsat the position 2 MHz deviated from the frequency spectra having 6 MHzseparation, that is, at the position of normal local oscillationfrequency (sweeping oscillation frequency) which is higher than carrierfrequency of video signal by intermediate frequency (58.75 MHZ), themarker signal is not affected by carrier frequency of audio signal orexternal noise. As a result, extremely stable channel selectionoperation is effected. Since no mechanically moving part is included,the apparatus provides a long life. It is also obvious that on-the-airchannel above or below the channel now being received may be selected bysimilar channel selection means.

Referring to FIG. 2 there is shown a channel selection apparatus forselectively selecting a channel of desired channel number and anon-the-air channel. The apparatus includes a channel selection key or adigit key 14 for selecting a particular channel desired, a sweepingswitch or a function key 2 for receiving onthe-air channels sequentiallyas described in connection with the embodiment of FIG. 1 or forreceiving onthe-air channel whose channel number is unknown,

-and an indicator 16 for indicating the channel number being received.To describe in more detail, added to the embodiment shown in FIG. 1 area memory circuit 15 for storing a channel number desired depending uponthe output of the channel selection switch 14 for selecting the desiredchannel, a counter circuit 17 for counting the marker signal pulses fromthe marker pulse generator circuit 10 when the set output O is appliedthereto from the first output terminal of the F.F. circuit 3 andsupplying the counting pulse to the channel number indicator 16 and thememory circuit 15, a comparator circuit l8 for comparing the output ofthe counter circuit with the stored content of the memory circuit 15, anOR circuit 19 having the output of the AND circuit 11 and the output ofthe comparator circuit as inputs and supplying its output to the resetterminal R of the F.F. circuit 3, and an OR circuit 13 having the outputof the function key 2 and the output of digit key 14 as inputs andsupplying its output to the set terminal S of the F.F. circuit.

Assuming that the digit key 14 is set to N channel (N being l3, l4, 62,for example), the memory circuit 15 stores a numeric value correspondingto the channel number N. At the same time, the signal from the digit key14 is fed through the OR circuit 13 to the set terminal S of the F.F.circuit 3 so that, as described in FIG. 1, the sweeping oscillator 1starts its oscillation and the frequency gradually increases from 528MHz which is 2 MHz below the lowest channel frequency. As described inFIG. 1, by the cooperation of the harmonics generator 6, the mixer 5,the band pass amplifier 7 and the detector circuit 9, the (2n-l )thsignal (where n=l 2, 50) from the outputs of the detector circuit 9 isderived from the pulse generator circuit 10 as marker signal, which issupplied to the AND circuit sequentially. The marker signals are thencounted by the counter circuit 17 sequentially. For each count, thecount of the counter circuit 17 and the preset value stored in thememory circuit are compared at the comparator circuit 18. When theoutput frequency of the sweeping oscillator 1 reaches the frequencycorresponding to the N channel to be selected, that is, when the numberof the marker signal pulses counted by the counter circuit 17 reaches(2N25), where N=l3, l4, l5, 62, the number of the marker signal pulsessupplied to the comparator circuit 18 corresponds to the numeric valuepreset to the memory circuit 15 and the stop-of-sweep signal is suppliedfrom the comparator circuit 18 through the OR circuit 19 to the resetterminal R of the FF. circuit 3. When the F.F. circuit is reset, thesweep of the sweeping oscillator stops and the AFC circuit 8 operates asdescribed in connection with FIG. 1. Since the count of the countercircuit 17 at the time of the stop-of-sweep corresponds to the selectedchannel number, i.e., the N channel, the indicator circuit 16 canindicate the channel number which has been selected. In the presentembodiment, it is clear that the on-the-air channel may be received bythe operation of the function switch 2 as in the embodiment of FIG. 1.

Simultaneously with the stop-of-sweep, the signal from the firstterminal of the F.F. circuit 3 is passed to the counter circuit 17 tocause the memory circuit 15 to store the count of the counter circuit17. The memory circuit 15 is made up of non-volatile memory cells andhence the channel selection of the channel previously stored in thememory circuit 15 is achieved simultaneously with the power-on sequenceso that when the power is switched on again the channel which has beenreceived before can be again received either by the use of the functionswitch 2 or the digit switch 14.

The embodiment shown in FIG. 3 contemplates to simplify overall circuitarrangement of the TV receiver set by permitting the insertion of themixer and the band pass amplifier, etc., shown in FIGS. 1 and 2 into anantenna circuit. For this purpose, there is provided means for switchingthe output of the harmonics generator 6 and the output of the antenna 20by means of a switch 21 and supply it to the mixer 5 through a highfrequency amplifier 22. The harmonics generator 6 multiplies the outputof a reference frequency oscillator 23 comprising a crystal to producefrequency spectra having frequency separation equal to the frequencyseparation between each channel. The switch 21 is connected to theharmonics generator 6 until the desired channel is selected. Aftercompletion of the channel selection, the antenna 20 is connected to thehigh frequency amplifier 22 by a switching means to be described later.The high frequency amplifier 22, the mixer 5 and the intermediatefrequency amplifier 24 which amplifies an intermediate frequencydelivered from said mixer 5 are all used in selecting a channel as wellas in receiving the image of said selected channel. The output of theintermediate frequency amplifier 24 is fed to the detector circuit. Whena desired channel button of the digit key 14 is depressed to select adesired channel, the numeric value corresponding to the desired channelis set to the counter circuit 17a and at the same time the harmonicsgenerator 6 is connected to the high frequency amplifier 22 by means ofthe output of the digit key. The sweeping generator 1 is driven by a DCoutput voltage from the sweep voltage generator 4a and varies its outputfrequency depending upon the DC voltage. Simultaneously with theoperation of the digit key 14 the start-to-sweep signal is applied viathe counter circuit 17a to the sweep voltage generator circuit 4a. Sincethe sweep voltage generator 4a applies saw-tooth sweep voltage to thesweeping oscillator the output frequency of the sweeping oscillatorvaries continuously. As stated above, the mixer 5 produces a beat whichis generated each time a predetermined relationship is obtained betweenthe output frequency of the harmonics generator 6 and the outputfrequency of the sweeping oscillator 1. The beats are passed through theintermediate frequency amplifier 24 and only those beats which have apredetermined frequency are taken out, which beats are then rectified bythe rectifier 25 and applied to the counter 17a.

When the numeric value set by the operation of the digit key 14 and thecount of the number of the beats coincide, the counter circuit 170applies a first stop-ofsweep signal to the sweep voltage generator 4a tostop the sweep of the sweeping oscillator I and simultaneously appliessignal 27 to the switch 21 to connect the antenna to the high frequencyamplifier 22. The output frequency of the sweeping oscillator l is nowfixed to the frequency capable of receiving the desired channel. Sincethe output of the rectifier is applied to a frequency correctionterminal of the sweeping oscillator l, the signal passing through theband pass amplifier 7 and the rectifier 25 after reception preventsfrequency variation of the sweeping oscillator I.

An example of the switch 21 is shown in FIG. 4 in which the antenna 20is connected to an electromagnetic coil 30 through the amplifier 28 andan electronically operated switch 29, and the output terminal of theharmonics generator 6 is connected to an electromagnetic coil 34 throughan amplifier 32 and an electronically operated switch 33, and an inputterminal of the high frequency amplifier 22 is connected to anelectromagnetic coil 35, the coils 30, 34 and 35 beingelectromagnetically coupled. By supplying the signal 26 from the digitkey 14 to the switch 29 to open it, electromagnetically coupling onlythe electromagnetic coils 34 and 35, supplying the signal 27 from thecounter 17a to the switch 33 to open it and electromagnetically couplingonly the coils 30 and 35, the switching of the switch 21 isaccomplished. An undesirable high frequency coupling between the antennaoutput terminal and the output terminal of the harmonics generator isavoided, if necessary, by a suitable shielding means or isolator means.

For the purpose of prevention of counting error due to the entry ofunwanted harmonics into the mixer 5 during the sweep of the sweepingoscillator l and the improvement of the amplification factor during thereception and the prevention to mixed modulation, it is desirable forthe high frequency amplifier 22 to employ a tuning type in which theoutput of the sweeping oscillator l is coupled together.

The arrangement of the sweep voltage generator 4a and the waveforms forillustrating the operation thereof are shown in FIGS. 6 and 7,respectively. The illustrated sweep voltage oscillator includes areversible counter for counting input clock pulses either incrementallyor decrementally and a D-A converter for converting the count of thecounter to a DC. voltage. As shown in FIG. 7, during the sweep of thesweeping oscillator l, discrete saw-tooth waves 38 are produced by theinput pulses 37, and when the supply of the input pulses 37 is ceased bythe stop-of-sweep signal from the counter circuit 170, the outputthereof is maintained at a fixed DC. voltage level 39 which correspondsto the level of the saw-tooth wave at the instant the input pulse hasbeen ceased'.

The sweep voltage generator 4a comprises, as shown in FIG. 6, a seriesconnection of a plurality of F.F. circuits such as FFl FF7, and therespective output terminals TI T7 of those F.F. circuits have respectiveresistors R1 R7 connected thereto. There exists a relationship 2R,,,=R,, (n==l, 2, 3, between the resistance values of the respectiveresistors. CP designates an input terminal for the pulse 37, FWrepresents a signal input terminal for obtaining forward sweep voltage(see FIG. 7F), and BW represents a signal input terminal for obtainingbackward sweep voltage (see FIG. 78). By selectively supplying thechannel selection signal to those terminals, it is possible to increaseor decrease the output frequency of the sweeping oscillator 1. Controlsignal for the sweep is supplied from the terminal 40 to the sweepingoscillator 1.

While the embodiment of FIG. 3 shows the apparatus for selecting adesired channel, in actual case, there may be those channels among anumber of channels through which no electric -wave are being transmittedand there may be a case where operator or user does not remember thechannel number which he wishes to select. Accordingly, there exist manycircumstances 'where the selection of an on-the-air channel is desiredor the sequential selection of the on-the-air channels only is desired.FIG. 5 shows an embodiment contemplated to meet such a requirement.

In this embodiment, a digit and function key 41 is so arranged that,when a digit key corresponding to a desired channel number is depressed,it produces a first channel selection signal (individual channelselection signal) 42 corresponding to the desired channel and a secondchannel selection signal (search channel selection signal) 43 forselecting only on-the-air channels when the function key is depressed.The first channel selection signal 42 is applied to the counter 17a toset the numeric value corresponding to the desired channel number to thecounter. The second channel selection signal 43 is applied to the setterminal S of the F.F. circuit 44. Outputs from the NAND circuits and 46are conducted to the NOR circuit 47. Outputs from said NOR circuit 47and the OR circuit 48 are supplied to the reset terminal R and thgetterminal S of the F.F. circuit 49..The reset output 0, of the F.F.circuit 44 and the output of the counter 17a are applied to the NANDcircuit 45 as inputs, and the set output Q of the F.F. circuit 44 andthe output of the rectifier 25 are applied to the NAND circuit 46 asinputs. The output of the rectifier 25 is also applied to the counter17a as count pulse. The outputs of the NAND circuits 45 and 46 areapplied to the NOR circuit 47 as inputs, and the output of the NORcircuit 47 and the output of the OR circuit 48 are applied to the resetterminal R of the F.F. circuit 49 and the set terminal S, respectively.There are further provided a clock pulse generator 51, AND circuits 52,53 and 54, and OR circuit 55 and an OR circuit 56 bearing three inputterminals. The AND circuit 52 receives the set output 0, of the F.F.circuit 49 and the clock pulse from the clock pulse generator 51 as itsinput, and the AND circuit 53 receives the reset output 6 of the F.F.circuit 49 and a signal 57 to be described later as its inpu t, and theAND circuit 54 receives the reset output 0 and a signal 58 to bedescribed later as its input. The reset output6 is also fed to the resetterminal R of the F.F. circuit 44. The OR circuit 55 receives the setoutput 02 of the F.F. circuit and the output of the AND circuit 53 asinputs,'and the output of the OR circuit 55 is applied to FW terminal(see FIG. 6) of the sweep voltage generator circuit 4a. The three-way ORcircuit 56 receives the outputs of the AND circuits 52, 53, 54 asinputs, and the output of the OR circuit 56 is applied to CP terminal,FIG. 6, of the sweep voltage generator circuit 4a. The output of the ANDcircuit 54 is also supplied to the BW terminal, FIG. 6, of the sweepvoltage generator circuit.

After the stop-of-sweep and the completion of the channel selection, itis possible, as described before, to correct the variation of the outputfrequency of the sweeping oscillator l for slight out-of-tuning bysupplying the output of the rectifier 25 to the frequency correctionterminal of the sweeping oscillator 1. However, the correction of theoutput frequency of the sweeping oscillator 1 due to substantialtemperatuare variation or external disturbance is difficult. For such acorrection, there are provided a reference frequency oscillator 59having oscillation frequency equal to the intermediate frequency ofthevideo signal carrier wave and a frequency discriminator 60 to which theoutputs of the band pass amplifier 7 and the counter 170 are applied.Also, the output signals 57 and 58, the details of which will bedescribed later, are applied to the input terminals of the AND circuits53, 54 respectively, whereby the output frequency of the sweepingoscillator l is maintained stably.

The operation of the above apparatus is now described. The F.F. circuits44 and 49 are in their reset status during a steady state or receivingstate. Under this circumstance, when a button of desired channel numberin the digit key 41 is depressed (i.e., individual channel selectionmode), the channel selection signal 42 thus developed serves to set thatchannel number to the counter 17a and at the same time set the F.F.circuit 49 via the OR circuit 48. Thus, 0, is set to 1 state so that theclock pulse from the clock pulse generator 51 is applied to the CPterminal of the sweep voltage generator 4a through the AND circuit 52and the OR circuit 56. At the same time, the output Q; (l) is fed to theFW terminal of the sweeping voltage generator circuit 4a through the ORcircuit 55 so that the sweep voltage generator circuit starts the sweepof the sweeping oscillator l in forward direction, that is, in thedirection of increasing output frequency. Simultaneously with theoccurrence of the first channel selection signal 42, the harmonicsgenerator 6 is connected to the high frequency amplifier 22 as in theembodiment of FIG. 3. Also as described before in connection with FIG.3, the beat is generated from the mixer 5. The marker signals passingthrough the band pass amplifier 7 appear at the rectifier 25. Since,however, the Q of the F.F. circuit 44 is 0, the marker signals do notpass through the NAND circuit 46, but are supplied to the counter 17a ascount pulses. When the counter 17a to which the channel number has beenpreset counts the predetermined number of marker pulses required toselect the particular channel, the output 50 is generated. Since the 6and Q of the F.F. circuit 44 are l and 0, respectively, when the signal50 appears, the signal 1 is supplied to the reset terminal R of the F.F.circuit 49 by the cooperation of the NAND circuits 45, 46 and the NORcircuit 47, and the F.F. circuit 49 is reset. As a result, the Q of theF.F. circuit 49 is switched to 0 and the clock pulse from the clockpulse generator 5liis no longer supplied to the CP terminal of the sweepvoltage generator 4 and the sweep is stopped. Since the O is l at thistime, the signals 57 and 58, to be described later, are supplied throughthe AND circuits 53, 54, the OR circuits 55, 56 to the terminals FW, BWand CP of the sweep voltage generator circuit 4a in order to accomplishfine tuning of the output frequency of the sweeping oscillator l.

The mode of operation for selecting on-the-air channels'only is nowdescribed. By depressing .a function key on the digit and function key41, the second channel selection signal 43 is generated. At the sametime, the antenna 20 is connected to the high frequency amplifier 22. Bythe second channel selec t ion'signal 43 the F.F. circuit 44 is set andthe Q, and 0, become I and 0,'respectively. The signal 0, (1) passesthrough t h 'e OR circuit 48 to set the F.F. circuit 49 and O and Q2become 1 and 0, respectively. At this time, no reset signal is appliedto the reset terminal R of the F.F. circuit 44. When the 0-,, becomes 1,the clock pulse from the clock pulse generator 51 is supplied throughthe AND circuit 52 and the OR circuit 56 to the C? terminal of the sweepvoltage generator 4a, and the signal Q2 (1) is supplied through the ORcircuit 55 to the FW terminal of the sweep voltage generator 4a. As aresult, the sweeping oscillator 1 starts its sweep in forward direction.After the initiation of the sweep, when the differential frequencybetween the frequency of the on-theair wave and the output frequency ofthe sweeping oscillator reaches a predetermined value, the output fromthe rectifier 25 at this instant causes the NAND circuit 46 and the NOR.circuit 47 (Q, being l) to reset the F.F. circuit 49 to tuurn Q2 and Oto O and 1, respectively. Thus, the supply of the clock pulse to thesweep voltage generator 4a is ceased and the sweep stops. in this case,the F.F. circuit 44 may be reset with the output 6 to facilitatesubsequent function key operation.

After completion of the channel selection by the function key, thefrequency variation of the sweeping oscillator 1 may be prevented by theoutput of the circuit comprising the band pass amplifier 7 and therectifier 25, as described above.

The operation of the reference frequency generator 59 and the frequencydiscriminator is now described. The output 50, that is, thestop-of-sweep signal and the output of the band pass amplifier 7 areapplied to the discriminator 60. If the intermediate frequency is higherthan the frequency of the reference frequency generator 59, thediscriminator producs the signal 58 which serves to decrease the outputvoltage of the sweep voltage generator 4a by AV which is proportional tothe difference between these frequencies, while if the former is lowerthan the latter the discriminator produces the signal 57 which serves toincrease by AV which is proportional to the differential frequency. Thediscriminator may be comprised of a reversible counter. The frequencydiscriminator 60, after it received broadcasting wave, starts itsoperation by the output of the band pass amplifier, and the signal 57 isapplied to the FW and CP termnals of the sweep voltage generator 4athrough the AND circuit 53 while the signal 58 is applied to the BW andCP terminals 'through the AND circuit 54 to stablize the frequency ofthe sweeping oscillator 1.

Referring to FIG. 8, another embodiment of the present invention isshown wherein means are provided to stabilize the frequency of thesweeping oscillator after the stop-of-sweep precisely and rapidly inresponse to the output frequency of the band pass amplifier. ln FIG. 8,the sweeping generator (local oscillator) 1 has its oscillationfrequency controlled by the output signal from the control signalgenerator 46, which is operated by the start-of-sweep signal sent from aprogramable counter 17b simultaneously with the activation of thefunction key 14. The output signal of the sweeping oscillator l ispassed to a frequency converter circuit, not shown, and alsosequentially mixed at the mixer 5 with the frequency spectra (528, 534,.822 MHz) having 6 MHz frequency separation supplied from the harmonicsgenerator 6. The output of the mixer 5 is supplied to the 2 MHZ bandpass amplifier 7 in which the signals near 2 MHZ only are amplified, asdescribed in connection with FIG. 1. Portion of the output of the bandpass amplifier 7 is fed to the detector 62 which in turn provides acount pulse or marker pulse to the programmable counter 17b each time itreceives the signal from the band pass amplifier. Other portion of theoutput of the band pass amplifier 7 is fed through a limiter circuit 64,a shaper circuit 65 and a gate circuit 66 to the counter 63. The gatecircuit 66 and the counter 63 are operated by the control signal fromthe control circuit 67 which in turn is activated when the count of theprogrammable counter 17b reaches a predetermined value, and the outputof the counter 63 is converted to DC. signal by a D-C converter, theconverted signal then being supplied to the control signal generator 46.

Assuming that the function key 14 is'operated to set the programmablecounter 17b to the numeric value corresponding to the N channel, underthis circumstance, the sweeping oscillator 1 receives the start-ofsweepsignal from the control signal generator 46, which starts itsoscillation from 528 MHz which is 2 MHzbelow the lowest channelfrequency and gradually increases the output frequency. The. detector 62supplies a count pulse to the programmable counter 17b each time itreceives 2 MHz signal from the band pass amplifier 7. When the frequencyof the sweeping oscillator 1 reaches the frequency corresponding to thedesired N channel, that is, when the number of the count pulsescorresponds to the preset value, the programmable counter 17b sends thestop-of-sweep signal to the control signal generator 46 to stop thesweep of the sweeping oscillator 1.

At the same time, control signal is fed from the programable counter 17bto the control circuit 67. The signal from the control circuit 67 servesto open the gate circuit 66 and the counter starts its operation. Thegate circuit 66 allows the 2 MHz signal pulse from the band passamplifier 7 to pass therethrough for the time interval T only. The 2 MHzsignal from the band pass amplifier then passes through the limitercircuit 64 and is shaped in the pulse shaper circuit 65. Thus, thecounter 63 counts the number of waves constituting the 2 MHz signals. Ifthe counted value number of waves in the time period T is higher than 2X X T, the signal which serves to decrease the oscillation frequency ofthe sweeping oscillator is fed from the D-A converter 12 tomaticfrequency control is referred to as digital AFC in the presentinvention.

With such digital AFC the range within which the frequency of thesweeping oscillator 1 can be drawn into the desired frequency even whenthe former deviates from the latter can be expanded considerably. As aresult, in the channel selection, where the sweeping rate of thesweeping oscillator l is designed higher or the channel selection rateis designed higher, it is possible -to rapidly control the oscillationfrequency of the sweeping oscillator to the desired value even if theformer substantially deviates from the latter. This makes it possible toshorten the channel selection time from on the order of 1 second, forexample, in the prior art to on the order of 0.1 second. Furthermore,since no factor which is subjected to the affect of externalperturbation such as pulsing noise and the like is included, thestability and the reliability of the operation are remarkably improved.

What is claimed is:

l. A local oscillation device for a television receiver set comprising:

a harmonics generator for producing simultaneously a plurality offrequency spectra having a frequency separation equal to the frequencyseparation among a plurality of channels, the frequency of each spectrumbeing an integral multiple of said separation frequency;

a sweeping oscillator for initiating its sweep in response to astart-of-sweep signal and varying its oscillation frequency;

means for supplying the output frequency from said sweeping oscillatorto a frequency converter which mixes said output frequency with atelevision broadcasting wave frequency to obtain a predetermined videointermediate frequency, said output frequency to be supplied to thefrequency convertor at a tuning condition not an integral multiple ofsaid separation frequency;

a mixer coupled to said harmonics generator and said sweeping oscillatorfor obtaining beat signals produced between the frequency ofsaidharmonics and the frequency of said sweep generator;

a band pass filter coupled to said mixer for deriving beat signals fromsaid mixer when a predetermined frequency difference exists betweenthe'output frequency of said harmonics generator and the outputfrequency of the sweeping oscillator;

means coupled to said band pass filter for deriving marker signalscorresponding to the respective channel positions from the output ofsaid band pass filter;

key means coupled to said sweep oscillator through a control means forproducing said start-of-sweep signal;

means for selecting a desired channel with the aid of said markersignals after the start-of-sweep and for stopping the sweep through saidcontrol means; and

an automatic frequency control (AFC) circuit for maintaining the outputfrequency of said sweeping oscillator constant after the stop-of-sweep.

2 The local oscillation device for a television receiver set as setforth in claim I wherein said band pass filter has a 2 MHz pass band.

3. The local oscillation device for a television receiver set as setforth in claim 1 wherein said means for being set to the numeric valuecorresponding to the channel to be selected by said digit key, saidstop-ofa harmonics generator for producing simultaneously 1 a pluralityof frequency spectra having a frequency separation equal to thefrequency separation among a plurality of channels, the frequency ofeach spectrum being an integral multiple of said separation frequency;

a sweeping oscillator for initiating its sweep in response to astart-of-sweep signaland varying its oscillation frequency;

means for supplying the output frequency from said sweeping oscillatorto a frequency converter which mixes said output frequency with atelevision broadcasting wave frequency to obtain a predetermined videointermediate frequency, said output frequency to be supplied to thefrequency convertor of a tuning condition not an integral multiple ofsaid separation frequency;

a mixer coupled to said harmonics generator and said sweeping oscillatorfor obtaining beat signals produced between the frequency of saidharmonics and the frequency of said sweep generator;

a band pass filter coupled to said mixer for deriving beat signals fromsaid mixer when a predetermined frequency difference exists between theoutput frequency of said harmonics generator and the output frequency ofthe sweeping oscillator;

means cupled to said band pass filter for deriving marker signalscorresponding to the respective channel positions from the output ofsaid band pass filter;

channel selection means including a digit key for supplying saidstart-of-sweep signal to said sweep oscillator through a control means,a counter for sequentially counting said marker signals and means forpresetting a numeric value corresponding to a channel number to beselected simultaneously with the channel selection operation forproducing a signal for stopping the sweep of said sweeping oscillatorwhenthe count of said counter corresponds to said preset value; and

an automatic frequency control (AFC) circuit for maintaining the outputfrequency of said sweeping oscillator constant after the stop-of-sweep.

5. The local oscillator device for a television receiver set as setforth in claim 4 wherein said channel selection means further includes amemory circuit and a comparator circuit, said memory circuit storing thechannel number to be selected by the operation of the digit key, saidcomparator circuit comparing the count of said counter with the storedcontent of said memory circuit for producing said stop-of-sweep signalwhen both values coincide.

6. The local oscillation device for a television receiver set as setforth in claim 4 further including an indicator circuit for indicatingthe channel number selected, the indicator circuit indicating thechannel number corresponding to the count of said counter.

7. The local oscillation device for a television receiver se t as setforth in claim 4 wherein said channel selection means includes a digitkey and a programmable counter, the count of said programmable countersweep signal being produced when the count of said counter reaches theset count of said programmable counter.

8. A local oscillation device for a television receiver set comprising:

a harmonics generator for producing simultaneously a plurality offrequency spectra having a frequency separation equal to the frequencyseparation among a plurality of channels, the frequency of each spectrumbeing an integral multiple of said separation frequency;

a sweeping oscillator for initiating its sweep in response to astart-of-sweep signal and varying its oscillation frequency;

means for supplying the output frequency from said sweeping oscillatorto a frequency converter which mixes said output frequency with atelevision broadcasting wave frequency to obtain a predetermined videointermediate frequency, said output frequency to be supplied to thefrequency convertor at a tuning condition not an integral multiple ofsaid separation frequency;

a mixer coupled to said harmonics generator and said sweeping oscillatorfor obtaining beat signals produced between the frequency of saidharmonics and the frequency of said sweep generator;

a band pass filter coupled to said mixer for deriving beat signals from.said mixer when a predetermined frequency difference exists between theoutput fre quency of said harmonics generator and the output frequencyof the sweeping oscillator,

means coupled to said band pass filter for deriving marker signalscorresponding to. the respective channel positions from the output ofsaid band pass filter,

a function key coupled to said sweep oscillator through a control meansfor producing said startof-sweep signal,

an AND circuit for producing an output only when said marker signal anda tuning signal from the TV receiver set occur concurrently,

means in response to the output of said AND circuit to stop the sweep ofsaid sweeping oscillator, and

and AFC circuit for maintaining the output frequency of said sweepingoscillator constant after the stop-of-sweep.

9. The local oscillation device for a television receiver set as setforth in claim 8 wherein said band pass filter has a 2 MHz pass band.

10. The local oscillation device for a television receiver set as setforth in claim 8 wherein said means for deriving the marker signalsincludes means for deriving marker signals corresponding to therespective channels from odd numbered or even numbered ones of said beatsignals.

11. A local oscillation device for a television receiver set comprising:

a harmonics generator for producing simultaneously a plurality offrequency spectra having a frequency separation equal to the frequencyseparation among a plurality of channels, the frequency of each spectrumbeing an integral multiple of said separation frequency;

a sweeping oscillator for initiating its sweep in response to astart-of-sweep signal and varying its oscillation frequency;

means for supplying the output frequency from said sweeping oscillatorto a frequency converter which mixes said output frequency with atelevision broadcasting wave frequency to obtain a predetermined videointermediate frequency, said output frequency to be supplied to thefrequency convertor at a tuning condition not an integral multiple ofsaid separation frequency;

a mixer coupled to said harmonics generator and said sweeping oscillatorfor obtaining beat signals produced between the frequency of saidharmonics and the frequency of said sweep generator;

a band pass filter coupled to said mixer for deriving beat signals fromsaid mixer when a predetermined frequency difference exists between theoutput frequency of said harmonics generator and the output frequency ofthe sweeping oscillator,

means coupled to said band pass filter for deriving marker signalscorresponding to the respective channel positions from the output ofsaid band pass filter,

channel selection means for producing a first stop-ofsweep signalincluding a digit key for producing said start-of-sweep signal, acounter for sequentially counting said marker signals and means forpresetting the numeric value corresponding to the channel number to beselected simultaneously with the channel selection operation forstopping the sweep of said sweeping oscillator when the count of saidcounter corresponds to said preset value,

means for producing said start-of-sweep signal through the operation ofa function key,

an AND circuit for producing an output only when said marker signal anda tuning signal from the TV receiver set occur concurrently,

means for producing a second stop-of-sweep signal for stopping the sweepof said sweeping oscillator in response to the output of said ANDcircuit, and

an automatic frequency control (AFC) circuit for maintaining the outputof said sweeping oscillator constant after the'stop-of-sweep.

12. The local oscillation device for a television receiver set as setforth in claim 11 further comprising a control circuit including a setterminal, reset terminal and first and second output terminals and acontrol signal generator circuit for said sweeping oscillator,

the signals from said function key and said digit key being applied tosaid set terminal,

said first and second stop-of-sweep signals being applied to said resetterminal of said control circuit,

the output from said first output terminal of said control circuit beingapplied to the input terminal of said control signal generator circuitto activate it, and

the output from the second output terminal of said control circuit beingapplied to said AFC circuit to activate the AFC circuit simultaneouslywith the stop-of-sweep.

13. A local oscillation device for a television receiver set comprising:

a harmonics generator for producing simultaneously a plurality offrequency spectra having a frequency separation equal to the frequencyseparation among a plurality of channels, the frequency of each spectrumbeing an integral multiple of said separation frequency;

a sweeping oscillator for initiating its sweep in response to astart-of-sweep signal and varying its oscillation frequency,

means for supplying the output frequency from said sweeping oscillatorto a frequency convertor which mixes said output frequency with atelevision broadcasting wave frequency to obtain a predetermined videointermediate frequency, said output frequency to be supplied to thefrequency convertor at a tuning condition not an integral multiple ofsaid separation frequency;

a mixer coupled to said harmonics'generator and said sweeping oscillatorfor obtaining beat signals produced between the frequency of saidharmonics and the frequency of said sweep generator;

a band pass filter coupled to said mixer for deriving beat signal fromsaid mixer when a predetermined frequency difference exists between theoutput frequency of said harmonic generator and the output frequency ofsaid sweeping oscillator,

means coupled to said band pass filter for deriving marker signalscorresponding to the respective channel positions from the output ofsaid band pass filter,

channel selection means including a digit key for producing saidstart-of-sweep signal, a counter for sequentially counting said markersignals and means for presetting the numeric value corresponding to thechannel selection operation for stopping the sweep of said sweepingoscillator when the count of said counter corresponds to said presetvalue, and

a digital automatic frequency control (AFC) circuit for counting thenumber of waves constituting the output signals from said band passfilter after the stop-of-sweep and controlling the output frequency ofsaid sweeping oscillator with said count so as to maintain the outputfrequency of said band pass filter at a predetermined frequency.

1. A local oscillation device for a television receiver set comprising:a harmonics generator for producing simultaneously a plurality offrequency spectra having a frequency separation equal to the frequencyseparation among a plurality of channels, the frequency of each spectrumbeing an integral multiple of said separation frequency; a sweepingoscillator for initiating its sweep in response to a start-of-sweepsignal and varying its oscillation frequency; means for supplying theoutput frequency from said sweeping oscillator to a frequency converterwhich mixes said output frequency with a television broadcasting wavefrequency to obtain a predetermined video intermediate frequency, saidoutput frequency to be supplied to the frequency convertor at a tuningcondition not an integral multiple of said separation frequency; a mixercoupled to said harmonics generator and said sweeping oscillator forobtaining beat signals produced between the frequency of said harmonicsand the frequency of said sweep generator; a band pass filter coupled tosaid mixer for deriving beat signals from said mixer when apredetermined frequency difference exists between the output frequencyof said harmonics generator and the output frequency of the sweepingoscillator; means coupled to said band pass filter for deriving markersigNals corresponding to the respective channel positions from theoutput of said band pass filter; key means coupled to said sweeposcillator through a control means for producing said start-of-sweepsignal; means for selecting a desired channel with the aid of saidmarker signals after the start-of-sweep and for stopping the sweepthrough said control means; and an automatic frequency control (AFC)circuit for maintaining the output frequency of said sweeping oscillatorconstant after the stop-of-sweep.
 2. The local oscillation device for atelevision receiver set as set forth in claim 1 wherein said band passfilter has a 2 MHz pass band.
 3. The local oscillation device for atelevision receiver set as set forth in claim 1 wherein said means forderiving the marker signals includes means for deriving signalscorresponding to odd numbered ones of even numbered ones of the beatsignals as said marker signals correspond to the respective channels. 4.A local oscillation device for a television receiver set comprising: aharmonics generator for producing simultaneously a plurality offrequency spectra having a frequency separation equal to the frequencyseparation among a plurality of channels, the frequency of each spectrumbeing an integral multiple of said separation frequency; a sweepingoscillator for initiating its sweep in response to a start-of-sweepsignal and varying its oscillation frequency; means for supplying theoutput frequency from said sweeping oscillator to a frequency converterwhich mixes said output frequency with a television broadcasting wavefrequency to obtain a predetermined video intermediate frequency, saidoutput frequency to be supplied to the frequency convertor of a tuningcondition not an integral multiple of said separation frequency; a mixercoupled to said harmonics generator and said sweeping oscillator forobtaining beat signals produced between the frequency of said harmonicsand the frequency of said sweep generator; a band pass filter coupled tosaid mixer for deriving beat signals from said mixer when apredetermined frequency difference exists between the output frequencyof said harmonics generator and the output frequency of the sweepingoscillator; means cupled to said band pass filter for deriving markersignals corresponding to the respective channel positions from theoutput of said band pass filter; channel selection means including adigit key for supplying said start-of-sweep signal to said sweeposcillator through a control means, a counter for sequentially countingsaid marker signals and means for presetting a numeric valuecorresponding to a channel number to be selected simultaneously with thechannel selection operation for producing a signal for stopping thesweep of said sweeping oscillator when the count of said countercorresponds to said preset value; and an automatic frequency control(AFC) circuit for maintaining the output frequency of said sweepingoscillator constant after the stop-of-sweep.
 5. The local oscillatordevice for a television receiver set as set forth in claim 4 whereinsaid channel selection means further includes a memory circuit and acomparator circuit, said memory circuit storing the channel number to beselected by the operation of the digit key, said comparator circuitcomparing the count of said counter with the stored content of saidmemory circuit for producing said stop-of-sweep signal when both valuescoincide.
 6. The local oscillation device for a television receiver setas set forth in claim 4 further including an indicator circuit forindicating the channel number selected, the indicator circuit indicatingthe channel number corresponding to the count of said counter.
 7. Thelocal oscillation device for a television receiver set as set forth inclaim 4 wherein said channel selection means includes a digit key and aprogrammable counter, the count of said programmable counter being setto the numeric Value corresponding to the channel to be selected by saiddigit key, said stop-of-sweep signal being produced when the count ofsaid counter reaches the set count of said programmable counter.
 8. Alocal oscillation device for a television receiver set comprising: aharmonics generator for producing simultaneously a plurality offrequency spectra having a frequency separation equal to the frequencyseparation among a plurality of channels, the frequency of each spectrumbeing an integral multiple of said separation frequency; a sweepingoscillator for initiating its sweep in response to a start-of-sweepsignal and varying its oscillation frequency; means for supplying theoutput frequency from said sweeping oscillator to a frequency converterwhich mixes said output frequency with a television broadcasting wavefrequency to obtain a predetermined video intermediate frequency, saidoutput frequency to be supplied to the frequency convertor at a tuningcondition not an integral multiple of said separation frequency; a mixercoupled to said harmonics generator and said sweeping oscillator forobtaining beat signals produced between the frequency of said harmonicsand the frequency of said sweep generator; a band pass filter coupled tosaid mixer for deriving beat signals from said mixer when apredetermined frequency difference exists between the output frequencyof said harmonics generator and the output frequency of the sweepingoscillator, means coupled to said band pass filter for deriving markersignals corresponding to the respective channel positions from theoutput of said band pass filter, a function key coupled to said sweeposcillator through a control means for producing said start-of-sweepsignal, an AND circuit for producing an output only when said markersignal and a tuning signal from the TV receiver set occur concurrently,means in response to the output of said AND circuit to stop the sweep ofsaid sweeping oscillator, and and AFC circuit for maintaining the outputfrequency of said sweeping oscillator constant after the stop-of-sweep.9. The local oscillation device for a television receiver set as setforth in claim 8 wherein said band pass filter has a 2 MHz pass band.10. The local oscillation device for a television receiver set as setforth in claim 8 wherein said means for deriving the marker signalsincludes means for deriving marker signals corresponding to therespective channels from odd numbered or even numbered ones of said beatsignals.
 11. A local oscillation device for a television receiver setcomprising: a harmonics generator for producing simultaneously aplurality of frequency spectra having a frequency separation equal tothe frequency separation among a plurality of channels, the frequency ofeach spectrum being an integral multiple of said separation frequency; asweeping oscillator for initiating its sweep in response to astart-of-sweep signal and varying its oscillation frequency; means forsupplying the output frequency from said sweeping oscillator to afrequency converter which mixes said output frequency with a televisionbroadcasting wave frequency to obtain a predetermined video intermediatefrequency, said output frequency to be supplied to the frequencyconvertor at a tuning condition not an integral multiple of saidseparation frequency; a mixer coupled to said harmonics generator andsaid sweeping oscillator for obtaining beat signals produced between thefrequency of said harmonics and the frequency of said sweep generator; aband pass filter coupled to said mixer for deriving beat signals fromsaid mixer when a predetermined frequency difference exists between theoutput frequency of said harmonics generator and the output frequency ofthe sweeping oscillator, means coupled to said band pass filter forderiving marker signals corresponding to the respective channelpositions from the output of said band pass filter, channel selectionmeans for producing a first stop-of-sweep signal including a digit keyfor producing said start-of-sweep signal, a counter for sequentiallycounting said marker signals and means for presetting the numeric valuecorresponding to the channel number to be selected simultaneously withthe channel selection operation for stopping the sweep of said sweepingoscillator when the count of said counter corresponds to said presetvalue, means for producing said start-of-sweep signal through theoperation of a function key, an AND circuit for producing an output onlywhen said marker signal and a tuning signal from the TV receiver setoccur concurrently, means for producing a second stop-of-sweep signalfor stopping the sweep of said sweeping oscillator in response to theoutput of said AND circuit, and an automatic frequency control (AFC)circuit for maintaining the output of said sweeping oscillator constantafter the stop-of-sweep.
 12. The local oscillation device for atelevision receiver set as set forth in claim 11 further comprising acontrol circuit including a set terminal, reset terminal and first andsecond output terminals and a control signal generator circuit for saidsweeping oscillator, the signals from said function key and said digitkey being applied to said set terminal, said first and secondstop-of-sweep signals being applied to said reset terminal of saidcontrol circuit, the output from said first output terminal of saidcontrol circuit being applied to the input terminal of said controlsignal generator circuit to activate it, and the output from the secondoutput terminal of said control circuit being applied to said AFCcircuit to activate the AFC circuit simultaneously with thestop-of-sweep.
 13. A local oscillation device for a television receiverset comprising: a harmonics generator for producing simultaneously aplurality of frequency spectra having a frequency separation equal tothe frequency separation among a plurality of channels, the frequency ofeach spectrum being an integral multiple of said separation frequency; asweeping oscillator for initiating its sweep in response to astart-of-sweep signal and varying its oscillation frequency, means forsupplying the output frequency from said sweeping oscillator to afrequency convertor which mixes said output frequency with a televisionbroadcasting wave frequency to obtain a predetermined video intermediatefrequency, said output frequency to be supplied to the frequencyconvertor at a tuning condition not an integral multiple of saidseparation frequency; a mixer coupled to said harmonics generator andsaid sweeping oscillator for obtaining beat signals produced between thefrequency of said harmonics and the frequency of said sweep generator; aband pass filter coupled to said mixer for deriving beat signal fromsaid mixer when a predetermined frequency difference exists between theoutput frequency of said harmonic generator and the output frequency ofsaid sweeping oscillator, means coupled to said band pass filter forderiving marker signals corresponding to the respective channelpositions from the output of said band pass filter, channel selectionmeans including a digit key for producing said start-of-sweep signal, acounter for sequentially counting said marker signals and means forpresetting the numeric value corresponding to the channel selectionoperation for stopping the sweep of said sweeping oscillator when thecount of said counter corresponds to said preset value, and a digitalautomatic frequency control (AFC) circuit for counting the number ofwaves constituting the output signals from said band pass filter afterthe stop-of-sweep and controlling the output frequency of said sweepingoscillator with said count so as to maintain the output frequency ofsaid band pass filter at a predetermined frequency.